Publish/Subscribe, or simply pub/sub, is an asynchronous messaging paradigm. There may be any number of publishers and subscribers. Each publisher may publish any number of messages. However, a publisher is not programmed to send its messages to specific subscribers. Instead, the messages are grouped into any number of classes, often called “topics”. That is, each message published by a publisher may belong to one or more of the topics. Each subscriber may express interest in one or more of the topics and receive messages belonging to those specific topics. In this sense, a subscriber subscribes to the specific topics of interest and receives only the messages belonging to those topics it subscribes. Alternatively, each subscriber may specify one or more content filters and receive messages that match to those content filters. Of course, an entity may be both a publisher and a subscriber, as the same entity may both publish messages and subscribe to topics.